Details
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Bug
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Status: Closed
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Major
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Resolution: Fixed
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0.10.0, 0.11.0
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None
Description
The current implementation of Flajolet-Martin estimator to estimate the number of distinct values doesn't use hash functions that are pairwise independent. This is problematic because the input values don't distribute uniformly. When run on large TPC-H data sets, this leads to a huge discrepancy for primary key columns. Primary key columns are typically a monotonically increasing sequence.